The invention relates to formwork for surfaces varying in curvature, including a face sheet adjustable with respect to its curvature, including girders supporting the face sheet and further including a boom system composed of individual boom members applied to the girders in spaced relationship to the face sheet, the effective length of the boom members between the girders and their points of application being adjustable at the girders to change the curvature of the face sheet, and mutually opposed formwork elements being adapted to be braced by means of formwork anchor ties.
Such formwork is known from German Patent Specification No. 24 26 708. In that reference, the boom members are formed by oppositely threaded tie rods engaging with a threaded sleeve on either side, so-called turnbuckles, rotation of the sleeve bringing about the desired change in length. On account of the distance of the boom members from the face sheet, the curvature of the face sheet can be changed through such a change in length. In each case one end of the rod engages a girder and it is necessary for the mutually opposed girders of the formwork elements to be braced together by means of formwork anchor ties in order that the distances of the mutually opposed formwork elements are maintained, particularly when the concrete is being poured in. This formwork has proved successful, but requires a relatively large number of formwork anchor ties because these are present on each girder.
Formwork having a face sheet changeable with respect to its curvature is already known from European Patent Specification No. 0 139 820, in which no formwork anchor ties whatsoever are provided for the mutually opposed formwork elements. This signifies, however, that the formwork elements of the mutually opposed surfaces are completely separate from each other, so that the slightest inaccuracies during erection lead to deviations in the thickness of the wall to be concreted. In addition, during the process of concrete placement there is the danger that--through the concrete often poured in suddenly and quickly--formwork walls, which may initially have been accurately in position, become misaligned or moved. This likewise results in inaccuracies to the finished concrete wall.